1. Field of the Invention
The present invention relates to a connecting method of lenses for an imaging-device, a lens unit constructed by using the connecting method, and an imaging-device comprising the lens unit. More specifically, in a lens arrangement method for a lens unit composed of a plurality of lenses, the invention relates to a connecting method of lenses adjacent to each other in which the optical axis alignment of each of the lenses and the adjustment/correction of the lens-to-lens distance are easy and accuracy of the lens arrangement does not depend greatly on the shape of a lens housing.
2. Description of the Related Art
In recent years, it has been general to install an easy imaging-device to a mobile tool, such as a cell phone, a PDA and a laptop personal computer. And such imaging-device is required not only miniaturization but also higher-accuracy and higher quality for image recorded. In order to meet such requirements, for imaging elements such as CCD, C-MOS and the like, high-pixel designs are carried out. For optical lens systems, arranging of two or more lenses in combination is in trials to improve image quality. When a plurality of lenses are arranged in combination, the optical axis of each of the lenses should be arranged to be aligned in good accuracy to satisfactorily correct aberrant of the lenses. For this reason, methods of arranging a plurality of lenses in a lens housing with good accuracy have been studied.
In the conventional method for arranging a plurality of lenses in a lens housing, the methods fix to arrange each of the lenses by utilizing a shape in a lens housing formed on an inner wall of the lens housing. An example of such a lens arrangement is shown in FIG. 12.
FIG. 12 shows a sectional view of a lens unit 1 composed of three lenses in an optical axis direction. The lens unit is composed of a first convex lens 20, a first concave lens 21, a second convex lens 22, and a lens housing 8. As will be understood from FIG. 12, in order to fix to arrange the above-described three lenses in the certain positions respectively, a first tubing 26, a second tubing 27 and a third tubing 28 are provided with a certain diameter difference in an internal surface of the lens housing 8. Then each of the lenses 20, 21, 22 shaped to match the diameter of each of these tubings is sequentially arranged in the lens housing. Each of the lenses 20, 21, 22 inserted is arranged on each of the tubings 26, 27, 28 respectively. In this manner, each of the lenses is fixed to be arranged in the lens housing.
JP S62 153908 discloses a lens unit in which a plurality of lenses having a flange in an outer periphery portion which is thick in an optical axis direction to avoid affection on an image formation, are arranged in an optical axis direction. In the lens unit, the lenses are connected directly or indirectly via a spacer on side surfaces of flange to maintain a certain space, and the lenses are joined and fixed each other to maintain the relative positions. That is, the invention discloses a connecting method of lenses without using a lens housing by joining lenses together in the flange in which each of a flange in an outer periphery portion of the lenses are joined and fixed together.
JP 2004 205574 discloses “a lens unit comprising a first lens having a recess whose inner diameter is provided by the processing reference face of a first lens core die so as to have a lens core processing reference diameter; and a second lens having a projection whose outer diameter is provided by a second lens die having a processing reference diameter that is substantially the same as the lens core processing reference diameter, so as to have substantially the same lens core processing reference diameter. The projection of the second lens and the recess of the first lens are fitted together to connect the first and second lenses to each other.” That is, the invention discloses the method to join the first lens and the second lens by fixing in which the recess provided in an outer periphery portion of a lens core of the first lens and a projection provided in an outer periphery portion of a lens core of the second lens are fitted together to join and fix the lenses together.
JP S56 149010 discloses “a plastic lens having a depressed surface in an optical axis direction, which is formed in the shape of a circular-arc cone having a center in an optical axis.” That is, the invention discloses a method in which an outer periphery portion of a lens has a tapered surface in the form of a circular-arc cone having an axis in an optical axis, tapered surfaces of each of adjacent lenses are engaged with each other, depressed and fixed to connect the lenses together for arrangement.
JP 3739295 discloses an optical apparatus comprising a lens housing, a 1st lens being at least two or more lenses installed in the lens housing and having a conical surface with an optical axis as center at the rib inner wall part of the edge outer periphery part, and a 2nd lens having a conical surface engaged with the conical surface contacting to the rib inner wall part of the edge outer periphery part of the 1st lens with the optical axis as center on the rib outer wall part of the edge outer periphery part are prepared. The first lens has a vertical surface perpendicular to an optical axis and the lens housing has a vertical receiving surface abutting against a vertical surface of the first lens. The vertical surface of the first lens contact to the vertical receiving surface of the lens housing by inserting the first lens into the lens housing, and the conical surface of the inner wall of the rib on the first lens contact to the conical surface of the outer wall of the rib on the second lens to be installed in the lens housing. The second lens is fixed to the lens housing in such a manner that the edge outer periphery portion of the first lens is sandwiched by the circular-arc conical surface of the outer wall portion of the rib on the second lens and the vertical receiving surface of the lens housing. Due to the face contact of the conical surfaces, for the first lens and the second lens, a clearance is provided between opposed surfaces except the conical surfaces. The first lens and the second lens are simultaneously positioned in an optical axis and in an optical axis direction. That is, the invention discloses a method in which tapered surfaces formed in each of the lenses are utilized to join each other, whereby the lenses are connected together, and at the same time, the positioning of the lenses is finished and the lenses are joined and fixed together by contacting the outer periphery portion of each of the lenses to the inner wall surface of the lens housing.